The present invention relates to a pipe bending machine and substantially to such one that imparts a bend to the pipe along with an axial compression (upsetting) thereof, whereby the thickness of the pipe walls is not reduced.
This invention can be used to best advantage when applied to bending large-diameter steel pipes (1000 mm and over).
In the prior art, as a rule, a machine for bending large-diameter pipes is used comprising an overhanging bending mechanism provided with a grip and a braking arrangement. The pipe section to be bent is consecutively passed, by virtue of translational motion performed by the pipe under the action of the longitudinal travelling mechanism, through a heating appliance incorporating an electrical inductor, and through a sprayer-type cooling arrangement. Simultaneously with the pipe motion the bending mechanism with the end of the pipe being bent is turned. To provide upsetting of the pipe, the braking arrangement associated with the bending mechanism is used (cf., e.g., USSR Inventor's Certificate No. 183,034 Cl..49h, 18, 1966).
Because the braking arrangement develops an extra force directed oppositely to the pipe longitudinal motion, the power of the longitudinal travelling mechanism must be increased. The force developed by said mechanism is increased accordingly which presents a danger of buckling of the overhanging bending mechanism which holds the pipe being bent by means of a grip.
Attempts to obviate said shortcoming are widely known to have been made by virtue of a considerable increase in the rigidness of the bending mechanism by using a higher weight and larger size thereof.
However, such attempts only partially solve this problem, i.e., the diameter of the pipes being bent cannot exceed 630 mm, whereas in case of a larger pipe size, the weight and overall dimensions of the machine becomes unduly big.
The inventors have the knowledge of another machine for bending metal rods without upsetting, used in manufacturing curved furniture components. In this machine, the bending machine employs a bending mandrel which is rigidly connected with the teeth-carrying disk which is enveloped by a flexible tie member, viz., a chain connected to the longitudinal travelling mechanism (cf., e.g., French Pat. No. 1,215,829 Cl. 21d, 1960).
Notwithstanding the simplicity of its design, said machine is only applicable for small-radius pipe bending because the arm of application of a force to the pipe that is directed lengthwise to the longitudinal axis of the latter exceeds the distance from the point of contact of the chain with said disk to the pivot axis of the bending mechanism. As a result the translational velocity of the pipe portion being bent will inescapably exceed that of the pipe portion directly acted upon by the longitudinal travelling mechanism so that the pipe will be stretched, whereby the pipe walls within the portion being bent will be thinned.